This application claims the priority of German patent document 196 15 548.7, the disclosure of which is expressly incorporated by reference herein.
The invention relates to an ultrasound area surveillance system of the type used, for example, for monitoring the surroundings of vehicles to detect obstacles, or for monitoring the vehicle interior as a protection against theft.
In an area surveillance system of this type described in European Published Patent Application EP 0 326 623 A1, four ultrasonic transducer units are distributed along the front of an unmanned vehicle in a straight row at a considerable distance from one another. Directionally radiated ultrasonic wave fields from these transducers form detection lobes which extends toward the front of the vehicle, and can be used to detect obstacles which occur there. The radiating directions of the various transducer units are essentially parallel to one another, so that the width of the lobar detection area is not much larger than the distance of the exterior transducer units from one another.
For applications in which an approximately semicircular area is to be monitored, it is known to use a laser beam area surveillance system, which scans the desired detection area by means of a rotating laser beam. A system of this type is sold, for example, by the firm Leuze Electronic under the name rotoScan RS 3.
One object of the invention is to provide an ultrasound area surveillance system of the initially mentioned type which can monitor an approximately semicircular area as uniformly and completely as possible, at comparatively low cost.
The invention achieves this object by providing an ultrasound area surveillance system in which the ultrasonic transducer units are arranged in a closely adjacent manner, with their radiation directions extending to the outside in a fan shape. In this arrangement, the maximal width of the detection area swept by the radiated ultrasonic wave fields is typically several times larger than the spacing of adjacent transducer units, and much larger than the distance of the exterior transducer units from one another. The system can monitor a semicircular area reliably, without rotating parts. The ultrasonic transducer units can be arranged very compactly to implement the fan-shaped radiating directions, the individual transducer units being inclined with respect to one another and/or being arranged along a curved forward-arched line.
In one embodiment of the invention, a least one portion of the ultrasonic transducer units are arranged in a plane along a circular-arc-shaped line, for example, along a semicircular line, so that a corresponding sector area can be monitored.
In a further embodiment of the invention, ultrasonic transducer units are provided in two planes situated above one another, such that the ultrasonic wave field of a respective transducer unit of one plane is situated between, and partially overlaps, the ultrasonic wave fields of two adjacent transducer units of the other plane. By means of an arrangement of this type, the directionally radiated ultrasonic wave fields of the individual transducer units can comparatively homogeneously and completely sweep over a sector-shaped area. It is understood that the distance between adjacent transducer units situated on different planes is expediently comparatively narrow, as is the distance between adjacent transducer units on the same plane.
In another advantageous embodiment of the invention, each transducer unit of one plane is inclined or angled with respect to a pertaining transducer unit of the other plane about a normal axis and, as required, without any offsetting, is positioned such that its radiating direction is in each case situated in the center between the radiating directions of two adjacent transducer units of the other plane. This arrangement achieves a very homogeneous and complete ultrasonic wave coverage of the detection area.
In another advantageous embodiment, a reference wire is assigned to each transducer unit at a comparatively small distance, for the purpose of carrying out a function test. The analysis unit is configured, among other things, to detect ultrasonic waves which are deflected by the respective reference wires. It evaluates the presence of the reference wire waves as a prerequisite of a disturbance-free operation of the system. This prevents the system from being disabled in an unauthorized manner, for example, by plugging up the outlet areas of the transducer units. Furthermore, the presence of the reference wire waves supplies exact information concerning the state of a respective assigned electronic transmitting and receiving system.
By means of another embodiment of the invention, different desired surveillance distances (that is, surveillance areas of different sizes) can be implemented easily in that, while the ultrasonic wave radiation by the transducer units remains the same, a respective maximal transit time of reflected ultrasonic waves can be indicated in a variable manner in the analysis unit. Reflected ultrasonic waves whose transit time after the emission of an ultrasonic pulse by the transducer units is longer than the pertaining, variably predeterminable maximal transit time are not taken into account for the surveillance area or are at most treated differently than those whose transit time is shorter than the selected maximal transit time. As required, several surveillance areas with a different monitoring or warning intensity can therefore be defined, such as a near-field area with a high warning or protecting intensity and a remote-field area which adjoins toward the outside and has a lower warning intensity.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.